Between a transmitter and a detector of a fiber optic system, attenuation of the signal strength occurs. The system is designed for a normal amount of signal loss between transmitter and detector. At the detector, the signal strength must be maintained within an appropriate range. The minimum strength is determined by the need for an adequate signal-to-noise ratio. The maximum strength is determined by the need to avoid an overload of the detector.
In U.S. Pat. No. 5,325,459 issued to S. Schmidt in June, 1994 an optical attenuator is disclosed comprising a disk formed from two separate portions, a wedge shaped disk made of a light absorbing material affixed to a wedge shaped transparent disk. For adjusting different attenuations, the disk is rotated around an axis by a motor. The attenuator needs a complex setup to compensate for refraction and resulting beam deviations. The compensations ensure that the beam of light is coupled into the optical fiber at any angular orientation of the attenuator disk. As such, the device is expensive and prone to reliability problems.
A well known alternative to the complex solution disclosed in U.S. Pat. No. 5,325,459 is the use of an opaque straight edge disposed within the optical path of a collimated beam of light. Unfortunately, using this device for attenuating a beam of light results in a change of the polarization composition of the beam of light. This is an undesirable effect when used in an optical fibre network. Since polarization components of light within the system are often not known it is a disadvantage to have polarization dependent attenuation.
It would be advantageous to provide an attenuator that maintains the polarization composition of a beam of light.